Conventionally, potentiometers have been used in detecting rotational angles of electric valve actuators, and the like. Given the structure of the potentiometer, there is a tendency for the resistor to become damaged through wear by the slider, producing dust, where this is particularly severe in any sliding range that is used frequently. The result is that the slider becomes slightly dislocated, producing a phenomenon wherein a large change in the resistance value may occur suddenly. As a result, a large change in the potentiometer output signal may also occur suddenly, appearing as a spike signal S such as shown in FIG. 11. Note that in FIG. 11, the horizontal axis is the potentiometer dislocation (the slider dislocation) or angle, and the vertical axis is the magnitude of the output signal of the potentiometer.
When this type of spike signal appears in the output signal of the potentiometer, then there may be a sudden malfunction in the control operation of a control device that is operating based on the provision of this output signal. Given this, for example, in Japanese Examined Patent Application Publication H7-95081, the spike signal that appears in the output signal of the potentiometer is detected, and if the spike signal is greater than a specific upper limit value or less than a lower limit value, or if the rate of change of the spike signal is greater than a specific value, then this is evaluated as a failure. When the potentiometer is diagnosed with a failure, that the control devices, and the like, that operate based on the provision of the output signal thereof switch immediately to perform predetermined signal-failure control.
However, because the spike signals (noise), described above, are produced in an early stage of the changes in the potentiometer over time, the occurrence of this noise is not a problem, and thus there is a problem in that it is evaluated as a failure despite the ability to continue use thereafter. That is, in Japanese Examined Patent Application Publication H7-95081, only the single phenomenon of noise having occurred is captured, and evaluated as a failure in a stage that is too early, and thus there is a problem in that this reduces system uptime and causes expenses in terms of time and cost in replacing components.
The present invention is to solve such a problem, and an aspect of the present invention is to provide a potentiometer degradation evaluating method wherein it is possible to know, in a staged manner, the progress of the degradation in the performance of the potentiometer.